This disclosure relates to gas turbine engines, and more particularly to nacelle inlets for gas turbine engines.
Gas turbine engines, such as those used to power modern commercial and military aircraft, generally includes a fan section where an airflow is introduced to the gas turbine engine, a compressor section to pressurize the airflow, a combustor section for burning hydrocarbon fuel in the presence of the pressurized air, and a turbine section to extract energy from the resultant combustion gases. The airflow flows along a gaspath through the gas turbine engine. The gas turbine engine is typically enclosed in a nacelle, with the airflow introduced to the gas turbine engine at the fan via a nacelle inlet.
The nacelle inlet is utilized to smooth the airflow into the gas turbine engine, and is designed to reduce the airflow speed from upstream cruise speed of 0.8 Mach down to about 0.5 Mach. The typical nacelle inlet cross-section includes a throat at which the inlet diameter is at its narrowest and a diffuser section downstream of the throat, relative to the general flow direction of the airflow. The diffuser section typically slows the airflow just upstream of the fan.
A typical nacelle inlet is characterized by an inlet length (L), which is an axial length from a forwardmost point of the nacelle to a leading edge blade tip of the fan and a diameter (D) between opposing leading edge blade tips inlet. A conventional nacelle inlet has a ratio L/D of about 0.5. As gas turbine engine designs have evolved, designs have moved toward larger diameter fans, which require a greater inlet length to attain the L/D of 0.5. This increase in axial length of the nacelle increases overhang, adds weight and increases drag due to the nacelle, with all of these negatively affecting performance of the aircraft on which the gas turbine engine is utilized. To alleviate these issues, shorter inlet lengths have been proposed, increasing the amount of diffusion required per unit length to slow the incoming airflow to the desired 0.5 Mach.
It is often desired or necessary to remove fan blades from the fan for repair or replacement. It is desired to do this removal through the inlet with the inlet installed to minimize disassembly of the gas turbine engine. The shorter inlets, however, result in an inlet throat that is at a smaller radius than the fan radius, and because of the small throat radius and the nearness of the throat to the fan blades, removal of the fan blades may not be possible without removal of the inlet from the gas turbine engine.